We did this problem in undergraduate chemistry and I am very convinced of the theory. The fact is, as posted earlier, that the hot water melts the exesting ice and makes the resulting sheet continuous and there is no layering effect everytime that the Zamboni passes over the ice. Now, in contrast to the physical explanation given by others, the evaporation effect has very little to do with the quick freezing of the hot water. Cold water, placed on top of the ice, only contacts the ice at the exact water/ice interface. Hot water, on the other hand, melts down into the ice so that the water/ice interface is much greater than just on top of the ice/under the water. Because ice is less dense than water, that means that the molecular latice of ice has areas in it which are not filled and in fact are empty. The hot water molecules have a high energy and can, one melt the ice, but, also invade the emply spaces in the ice latice. When a hot water molecule invades this latice, it is surrounded on 5-6 sides by ice molecules. This hot water molecule quickly loses it's energy to the neighboring ice molecules and if the energy is not too great, then the ice stays ice and the hot water molecule becomes ice and expands into the ice latice. Thus further hot water molecules can invade this new latice. This process continues as the hot water molecules move down into the ice and finally each molecule has lost enough energy to become ice. The heat given off of the hot water molecules and absorbed by the ice molecules will raise the temperature of the ice. The refrigeration unit then cools the ice back down to playing temp. In short, the hot water molecules, being surrounded by ice molecules on almost all sides, are cooled quickly, whereas, cold water molecules would only be touching ice on one side and the heat transfer from cold water molecule to ice is 5-6 times less than it is with the hot water molecules. Evaporation may have a small effect, but the Zamboni puts down many, many gallons of water and they do not evaporate, nor lose enough energy through evaportation to account for the rapid freezing of water. To back up this statement, try freeze drying water. This is taking room temperature water or cold water and evaporating it under vacuum untill it freezes. This is a very slow process because the evaporation does not remove energy from the water very quickly. In effect the hot water in the Zamboni is is a surface phenomina and I would love to know who was brave enough to look at his fellow rink managers and say "Boys, I'm gonna put hot water on the ice, 'cause it's gonna freeze faster". Flame on. Jim Lawrence B.S. Chemistry 1988 Bemidji State University Ph.D. Biochemistry 1995 Purdue University